The present embodiments relate to a method for irradiation planning of a target volume and a method for irradiating a target region in a target volume.
Particle therapy is an established method for treating tissue (e.g., in tumor diseases). Irradiation methods of the kind employed in particle therapy are also used in non-therapeutic fields. For example, the non-therapeutic fields include research work such as for product development in the context of particle therapy done on inanimate phantoms or bodies, irradiation of materials, and so forth.
In these, charged particles such as protons, carbon ions, or other ions are accelerated to high energy levels, shaped into a particle beam, and carried via a high-energy transportation system to one or more irradiation chambers. In the irradiation chamber, the target volume to be irradiated is irradiated with the particle beam.
In the course of this, the target volume to be irradiated may move. For example, when a patient is being irradiated, motion of the patient while breathing may cause the tumor that is to be irradiated to move. Such a movement may also be simulated for research purposes by using model objects (e.g., phantoms).
In irradiation methods, in which many irradiation doses are to be deposited successively at different sites in the target volume and hence with a scanned particle beam, it is difficult to achieve a desired homogeneous dose distribution in the target volume if the target volume moves during the course of the irradiation.
With a scanned particle beam, the dose that is to be applied may be distributed among a plurality of passes. This method is also known as “rescanning.” A target region is approached multiple times. At the target region, the total dose is built up successively by a plurality of repeatedly applied individual doses during the rescanning passes. This has the advantage that errors in the dose deposition, which in the event of a single pass would lead to a completely mistakenly applied dose, are averaged out to a certain degree by the multiple rescanning passes. Uncertainties about the position of the target volume, movements of the target volume, and so forth, may thus be at least partially compensated for.
For improving this, the published presentation by Silvan Zenklusen, et al., titled “Preliminary investigation for developing repainted beam scanning on the psi gantry 2,” proposes that at each target point of a region that is scanned multiple times in a plurality of rescanning passes, in each rescanning pass, a dose that is less than an upper limit (e.g., an “upper dose limit”) is always applied. A target point is irradiated in consecutive rescanning passes until a set-point dose has been reached. In the ensuing rescanning passes, the target point is excluded form a further irradiation (e.g., the target point is no longer approached).